package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.WeakHashMap;
import java.util.BitSet;
import org.apache.lucene.index.IndexReader;

/** Constrains search results to only match those which also match a provided
 * query.  Results are cached, so that searches after the first on the same
 * index using this filter are much faster.
 *
 * <p> This could be used, for example, with a {@link RangeQuery} on a suitably
 * formatted date field to implement date filtering.  One could re-use a single
 * QueryFilter that matches, e.g., only documents modified within the last
 * week.  The QueryFilter and RangeQuery would only need to be reconstructed
 * once per day.
 *
 * @version $Id: QueryFilter.java 328729 2005-10-26 21:05:35Z yonik $
 */
public class QueryFilter extends Filter {
    private Query query;
    private transient WeakHashMap cache = null;

    /** Constructs a filter which only matches documents matching
     * <code>query</code>.
     */
    public QueryFilter(Query query) {
        this.query = query;
    }

    public BitSet bits(IndexReader reader) throws IOException {

        if (cache == null) {
            cache = new WeakHashMap();
        }

        synchronized (cache) { // check cache
            BitSet cached = (BitSet) cache.get(reader);
            if (cached != null) {
                return cached;
            }
        }

        final BitSet bits = new BitSet(reader.maxDoc());

        new IndexSearcher(reader).search(query, new HitCollector() {
            public final void collect(int doc, float score) {
                bits.set(doc); // set bit for hit
            }
        });

        synchronized (cache) { // update cache
            cache.put(reader, bits);
        }

        return bits;
    }

    public String toString() {
        return "QueryFilter(" + query + ")";
    }

    public boolean equals(Object o) {
        if (!(o instanceof QueryFilter))
            return false;
        return this.query.equals(((QueryFilter) o).query);
    }

    public int hashCode() {
        return query.hashCode() ^ 0x923F64B9;
    }
}
